One of the goals of plant genetic engineering is to produce plants with agronomically, horticulturally or economically important characteristics or traits. Traits of particular interest include high yield, improved quality and yield stability. The yield from a plant is greatly influenced by external environmental factors including water availability and heat, of which tolerance of extremes is in turn influenced by internal developmental factors. Enhancement of plant yield may be achieved by genetically modifying the plant to be tolerant to yield losses due to stressful environmental conditions, such as heat and drought stress.
Seed and fruit production are both limited inherently due to abiotic stress. Soybean (Glycine max), for instance, is a crop species that suffers from loss of seed germination during storage and fails to germinate when soil temperatures are cool (Zhang et al., Plant Soil 188: (1997)). This is also true in corn and other plants of agronomic importance. Improvement of abiotic stress tolerance in plants would be an agronomic advantage to growers allowing enhanced growth and/or germination in cold, drought, flood, heat, UV stress, ozone increases, acid rain, pollution, salt stress, heavy metals, mineralized soils, and other abiotic stresses.
Traditional breeding (crossing specific alleles of one genotype into another) has been used for centuries to increase abiotic stress tolerance and yield. Traditional breeding is limited inherently to the limited number of alleles present in the parental plants. This in turn limits the amount of genetic variability that can be added in this manner. Molecular biology has allowed the inventors of the instant invention to look far and wide for genes that will improve stress tolerance in plants. Protein phosphorylation is one of the major mechanisms controlling cellular functions in response to external signals in eukaryotes and kinases represent a large and diverse protein family. Protein kinases in plants have been shown to participate in a wide variety of developmental processes. Protein kinases also respond to environmental stresses
Members of the Snf1-related protein kinases play a major role in phosphorylation cascades involved in carbon assimilation in animals, fungi and plants. (Hardie D. G., Carling D. and Carlson M.; Ann. Rev. Biochem. 67: 821-855, 1998). Members of the AMP-activated/Snf1-related protein kinase subfamily are central components of highly conserved protein kinase cascades that now appear to be present in most, if not all, eukaryotic cells. Because the downstream targets of the action of these enzymes are many and varied, they have been discovered and rediscovered several times in different guises and by different approaches. Alderson and coworkers (Alderson A., et al. Proc. Natl. Acad. Sci. USA, 88: 8602-8605, 1991) cloned and sequenced a cDNA (RKIN1) encoding a Snf1 homolog from the higher plant rye. Transformation of an Snf1 mutant strain of yeast with a low-copy RKIN1 plasmid restored the ability to grow on nonfermentable carbon sources (Alderson A., et al. Proc. Natl. Acad. Sci. USA, 88: 8602-8605, 1991), showing that RKIN1 is functionally as well as structurally related to Snf1. Snf1 homologs were subsequently cloned from Arabidopsis thaliana (LeGuen L., Thomas M., Bianchi M., Halford N. G., and Kreis M., Gene 120: 249-254, 1992), barley, (Hannappel U., Vincente-Carbajosa J., Baker J. H. A., Shewery P. R., and Halford N. G., Plant Mol. Biol., 27: 1235-1240, 1995; Halford N. G., Vincente-Carbajosa J., Sabelli P. A., Shewery P. R., Hannappel U., and Kreis M., Plant J., 2: 791-797, 1992), tobacco (Muranaka T., Banno H., Machida Y., Mol. Cell. Biol. 14: 2958-2965, 1994) rice and maize (Ohba H. et al. Mo Genet., 263: 359-366, 2000). Two Snf1-related protein kinases from rice, OsPK4 and OsPK7, which are structurally very similar and share more than 75% homology with the wheat homolog WPK4, exhibit very different expression patterns as well as stress response in rice and maize plants (Ohba H. et al. Mo Genet., 263: 359-366, 2000). Based on yeast studies, Snf1 protein kinases including, OsPK4 and OsPK7, are expected to play a central role in energy metabolism to provide protection against environmental stress in the host organism. Very little or no changes were observed in the expression pattern of rice and maize OsPK7 genes in response to a variety of abiotic stresses such as light, nutrients, cold, drought, and salt. (Ohba H. et al. Mo Genet., 263: 359-366, 2000).
The current invention demonstrates and claims the utilization of the OsPK7 gene and its homologs to produce plants with enhanced abiotic stress tolerance, including response to suboptimal growth temperatures and amounts of water required for growth of natural plants.